1. Field of the Invention
This invention is related to an encryption communication method to prevent the theft and interception of, and tampering with, information in communication between computers; in particular, it relates to a method of encryption using an agent.
2. Description of the Related Art
In recent years, with the explosive spread of the Internet and intranets, the importance of information security has been steadily increasing. Known methods of security in information communication include the method of encryption of information using encryption keys that are possessed in common by terminals, such as the DES (Data Encryption Standard), and a method of encryption such as RSA in which terminals exchange public keys and information is encrypted using their private keys. In addition, to increase the safety of encryption, there are known methods such as changing the encryption key and encryption method over time, as described, for example, in Tokkaihei (Japanese Patent Disclosure) 1-212041.
In a conventional ordinary encryption communication system, the encryption method is public information. For this reason, in order to obtain a strong cryptosystem, the key used in encryption must have a large number of bits. However, when the key used in encryption has a large number of bits, the time required for encryption and decryption processing inevitably becomes long. In particular, when encryption is done in real time applications (such as voice and images) the slowness of the processing in conventional methods such as DES and RSA is a problem.
When encryption is done by a method that involves changing the combination of the encryption key and the encryption method over time, it is necessary to preregister the encryption key and preinstall the encryption program in the terminals that will be used for such encryption communication. Consequently, every time new terminal facilities are added in a network it is necessary to register the encryption key and install the encryption program in those terminals.